1. Field of Endeavor
The present invention relates to the field of thermal machines, and more specifically relates to a pressure casing.
2. Brief Description of the Related Art
Conventional bolted flange joints for pressure casings of thermal machines, as are reproduced in an example in FIG. 1, or of other installations with similar requirements, have a plurality of disadvantages which can be eliminated by the present invention. In the known pressure casing 20 from FIG. 1, two casing shells 20a and 20b are bolted together in a pressure-tight manner in a parting plane 21 via a flanges 23a, 23b . This is carried out by threaded bolts which, by a through-hole 27 in the upper casing shell 20a, are screwed into a threaded hole 26 in the lower casing shell 20b and, in this case, supported on the shoulder 28 in the process. Inside the bolted joint, a sealing lip 24 is arranged in the parting plane 21, and outside the bolted joint a support lip 25 is provided. On the inner side, provision can be made for a shield 22. The following disadvantages result from this arrangement:                During the warm-up phase of the pressure casing 20, during a cold start, the casing material which surrounds the threaded bolts heats up more quickly than the shank of the threaded bolts within the through-hole 27, which, on account of the different thermal expansion of the bolts and the casing, can lead to an overload and plastic elongation of the threaded bolts with subsequent local leakages.        At heavily loaded places, it can happen that the inner-lying sealing lip 24 is opened as a result of stresses in the casing wall, whereas the outer-lying support lip 25 is more heavily loaded because the torque created by the wall and the bolt forces has to be compensated by a higher counter-force on the support lip 25. Consequently, the necessary pressure upon the sealing lip 24 cannot be maintained any longer, in fact not even with larger bolts because with bolt diameters becoming larger the axis in which the bolt force acts is further away from the sealing lip 24 than in the case of smaller bolts, so that the leaktightness of the sealing lip 24 in actual fact is not improved.        In order to avoid a further increase of the bolt loading and to improve the situation described above, according to FIG. 1 the bolts are arranged so that their axes in the parting plane 21 of the flanged joint (tangentially) contact the center line 20c of the casing wall. This results in the inner side of the generally axially symmetrical (partially cylindrical or conical) casing 20 being disrupted in symmetry as a result of a deviation 29, which necessitates a special costly construction, for example for the inner shield 22.        